I'm doing a little research for a school project. How much hp does A/C take to run? Also do any of you know what pressure the high and low side run at? COPr and high and low temperatures would also be nice, but not necesary.

This is for my heat transfer class, we're learning about refrigeration cycles, and I'm going to map out the average automotive A/C system to see just how much heat it's capable of moving.

 

About 1 to 2 hp I believe on a serptine drive and about 3 to 5 on the old belt grives with fan cluthes.Just a guess.

 

That makes sense to me considering all the ecm has to do when it kicks on is add a few IAC counts to maintain idle. The way people make such a big deal of making sure the A/C is off when they race, you'd think it was like 50 hp, well maybe thats just the excuse the Honda guys make when ever I beat them by 20 car lengths.

 

I don't know the power numbers, but I keep the A/C off at the track because I get worried when the Mrs says the guys with the mops were wiping the track after my pass! (Condensation).

 

Most a/c systems shut themself's off at WOT. Yeah my track makes sure the street guys turn theirs off. I'm just looking for some numbers to play with.

 

A lot of folks say you can't feel 5 or 6 horsepower INCREASE.

I CAN FEEL a big DECREASE in power when I turn on the AC.

So, I'm going to guess closer to 7-8 HP to turn the AC compressor when it's engaged.

 

i think its more like 15 hp. i can feel my car run harder when the AC is on. i always have it off except when its about 95-110 out side.

 

I agree but figured the 1-2 hp guys would flame me outta here.

It's a LOT, that's for sure.

A little 2-3 horse Briggs & Stratton won't run it, that's for sure.

Mine is like setting the parking brake on "drag".

 

I was thinking more like 1-3 at idle, but I'm positive that would go up with rpm. Wish there was a way to really find out, I have a g-tech pro, but all of the vehicles I have available for testing turn the a/c off at full throttle.

 

My parking break doesn't have anything on my ac commpressor.

I figure that an R-4 compressor takes 30% of your total power.

 

Are we talking a 20 yr old a/c setup? Or when it was fresh from the factory? Because our cars took like .1hp when they were fresh out of the factory. The more wear, the more it takes to move it.

 

i've heard close to 10% power on belt drive

 

I always though people took their AC out to save weight & free up "some" HP. lower weight = faster times.

 

The AC in a car has the compressor turned by the engine, via the v/serp belt. From the viewpoint of the compressor, it doesn't care if the compressor is turned by an electric motor or by an internal combustion engine.

So, IMO you should be able to match the automotive AC unit (incl the volume of the cabin, and the potential for having 5 occupants plus the Florida/TX sun baking into the interior) to a small home electric-motor powered AC unit. For those units you can look up the electrical Watt consumption. From there 745 W = 1 hp..... so you should have a better estimate for the engine power load of the AC unit than just swagging it, by equating it to a small AC unit for home use. IMS you can also match the BTU (assuming they still use those units) of the home AC unit to the one *you* can estimate that's needed for the car interior.

Hints: avg person dumps 100 thermal watts into a car interior (1 person = 1 lightbulb model), and you need to assume worst-case southern summer weather, and the solar heating into the interior. That will tell you what the capacity is needed for the auto AC system.

I bet there are also numerous SAE articles on AC for automotive use, but I'll leave that search, and the nosediving into Thermo & Heat Xfer tables to you. I already did my time in those areas. HTH.

EDIT: FWIW I believe the high- and low-side pressures are printed in the FSM..... at least IIRC they are for the GM Bcars that I've had.

 

How many BTUs are the older a/c units? About 6-10,000 BTU? If you know the BTU rating you can use a conservative coeff. of performance to estimate the nominal power draw.

 

HA, I used to call the A/C button on my truck my NOS button. I'd turn off the AC for a boost of power.lol damn 4 banger trucks.

 

I totally forgot about the SAE papers. I just got my membership to SAE a couple of months ago, I should go check out the website.

 

My .02 here, don't notice any diff with AC on or off. Would like to remove it, though, just because I never use it, and all its hoses and whatnot take up space. I like the look of the AC delete pulley too. That's gotta free up a bit of power.